MULTILAYER POLYMER COMPOSITE FOR MEDICAL APPLICATIONS
Technical Field of the Invention
This invention relates to multilayer polymer structures or composites, and more
particularly to polymer multilayer thermoplastic composites for use in medical
applications. Background of the Invention
The thermoplastic multilayer polymer structures of this invention may be used in a variety of applications including for example, automotive and appliance
applications. However, the structures of the present invention are best suited for medical applications such as intravenous (IV) bags, tubing, etc. When preparing multilayer structures, the layers of the structures must adhere to each other. If the layers of the structure do not adhere to each other a glue, or tie
layer is used to stick the layers of the structure together. Layers which adhere to each other without a glue layer are useful and generally most desired.
Thermoplastics have been widely used in the formation of medical parts for
which excellent design, performance and volume capabilities are required. In order to
be useful in medical applications, a thermoplastic must meet various criteria. The
plastics must be inexpensive and easy to manufacture. The plastic should not react with or leach additives into physiologic solutions. The plastics must have resistance to degradation and/or deformation from steam, irradiation and ethylene oxide
sterilization techniques. The present invention serves to provide a material that
effectively meets these criteria.
Summary of the Invention
This invention relates to a multilayer thermoformable thermoplastic structure
5 comprising:
(A) a cap layer of a polymer composition comprising a homopolymer or
copolymer of polypropylene;
(B) a core or tie layer comprising a homopolymer of polypropylene; and
(C) an inner layer comprising: (i) from about 45 % to about 80% by weight
ιo of a homopolymer or copolymer of polypropylene or mixtures thereof; and (ii) from
about 15 % to about 40% by weight of an ethylene copolymer made using a metallocene
catalyst.
The multilayer structures of the present invention are useful in preparing
thermoformed articles, and are particularly useful in preparing parts or components for
i? use in medical applications, such as, for example, intravenous bags and tubing. The
layers of the multilayer structure do not require a glue or adhesive of any type and are
generally recyclable. Also, the multilayer structure of the present invention does not
contain any poly (vinyl chloride) ("PVC") and the related disposal problems of high
halogen content materials is thus not an issue. Furthermore, the structure of the
2c present invention does not rely on the use of expensive styrene-butadiene materials as
do many prior art medical thermoplastic compositions. Thus, the composition of the
present invention is substantially free of PVC and styrene-butadiene materials.
The foregoing and other features of the invention are hereinafter more fully
described and particularly pointed out in the claims, the following description setting
forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present
invention may be employed.
Description of the Preferred Embodiments
Unless the context indicates otherwise, throughout the specification and claims, the amount of the polymers present is determined exclusive of filler or other
nonpolymer additive in the polymer compositions. Therefore the amount of each
polymer is determined by dividing the weight of the polymer by the combined weight of all polymers present in the composition.
Cap Layer (A) The multilayer structure has an outside, top or cap layer (A). This cap layer comprises a polymer composition comprising a homopolymer or copolymer of
polypropylene. The number average molecular weight of the polypropylene polymers
is preferably above about 10,000 and more preferably above about 50,000. Such polypropylene polymers are preferably produced using a Ziegler catalyst. The
polypropylene polymers useful in preparing the polymer blends of the present invention
are well-known to those skilled in the art and many are commercially available.
Examples of such commercially available polypropylenes include Fina 8453, Aristech
F007S and F007F, Shell 7C06 and 5 A97, Exxon PD7/32, Lyondell X0200 and X0201 ,
Aristech 4007F and 4040F (copolymer of propylene and ethylene) and Quantum
PP8479HV. Preferably, for many medical applications such as IV bags the cap layer
comprises a random copolymer of polypropylene. An example of such a random
copolymer is a material sold by Rexene under the trade designation PP 23M2.
Core Layer (B)
The multilayer structure also contains a core or tie layer that is disposed
between the cap layer (A) and the inner layer (C). This core layer comprises a
homopolymer of polypropylene. The homopolymer has a tensile modulus of less than 100,000 psi and preferably, at least 10% by weight of the homopolymer displays an
amorphous structure. Such materials are known as flexible polyolefins. An example of a homopolymer suitable for use in the present invention is a homopolymer sold by
Rexene under the trade designation WHO.
Inner Layer (C) The multilayer structure also contains an inner layer. In many applications this
inner layer serves as a sending layer to prevent the migration of water and other liquids
through the structure. The inner layer comprises: (i) from about 45 % to about 80% ,
and preferably from about 50% to about 70% by weight of a homopolymer or
copolymer of polypropylene or mixtures thereof; and (ii) from about 15 % to about 40% , and preferably from about 20% to about 35 % by weight of an ethylene
copolymer made using a metallocene catalyst.
The number average molecular weight of the polypropylene polymers is
preferably above about 10,000 and more preferably above about 50,000. Such
polypropylene polymers are preferably produced using a Ziegler catalyst. The
polypropylene polymers useful in preparing the polymer blends of the present invention
are well-known to those skilled in the art and many are commercially available.
Examples of such commercially available polypropylenes include Fina 8453, Aristech
F007S and F007F, Shell 7C06 and 5A97, Exxon PD7/32, Lyondell X0200 and X0201,
Aristech 4007F and 4040F (copolymer of propylene and ethylene) and Quantum
PP8479HV.
The component (ii) comprises an ethylene copolymer made using a metallocene
catalyst or an equivalent single site metal catalyst. Such copolymers include ethylene-
butene, propylene, hexene or octene copolymers made using a metallocene or
equivalent single site catalyst. Such ethylene copolymers suitable for use in the present
invention display a melting point below about 105 °C. Such ethylene-butene or hexene
copolymers are available commercially from Exxon Chemicals of Houston, Texas,
under the trade designation Exact. An example of a preferred commercially available
ethylene copolymer suitable for use in the present invention is a saturated ethylene-
octene copolymer sold under the trade designation Engage 8100 by DuPont Dow
Elastomers of Wilmington, Delaware.
Fillers
The above polymer layers may contain one or more fillers of the type used in
the polymer art. Examples of fillers employed in a typical compounded polymer blend
according to the present invention include talc, calcium carbonate, mica, wollastonite,
dolomite, glass fibers, boron fibers, carbon fibers, carbon blacks, pigments such as
titanium dioxide, or mixtures thereof. The amount of filler included in the blended
polymers may vary from about 0% to about 20% of the combined weight of polymer
and filler. Generally amounts from about 5 % to about 15 % , from about 0% to about
4%, may be included. However, for many medical applications, preferably the layers
contain less than 1 % by weight filler and are preferably substantially free of fillers.
The fillers may be treated with coupling agents to improve the bond between
the fillers to the resin. For example, the fillers can be treated with materials such as
fatty acids (e.g., stearic acid), silanes, maleated polypropylene, etc. The amount of
coupling agent used is an amount effective to improve the bond between the fillers with
the resin. However, once again, it will be appreciated that in many medical
applications, it is generally preferred that no fillers be included in the layers.
Miscellaneous Additives
Various additives may be included in the polymer compositions of the layers at
various rates of addition. Such additives include, for example, light stabilizers, heat
stabilizers, antioxidants, lubricants, colorants, pigments, etc. Generally, additives are
included in the polymer blend at a rate of less than 10 % by weight, and preferably less
than 3 % by weight, and more preferably less than 1 % by weight of the polymer blend
composition. However, for medical applications, preferably additive additions are kept
to a minimum or are substantially free of any type of additives.
Additional Polymers
It will be appreciated that polymer compositions of the various layers made in
accordance with the present invention may include one or more additional polymeric
materials such as, for example elastomers or rubbers such as silicone rubbers or
styrene-butadiene materials, maleated materials, styrenic materials, etc. These
additional polymers would be present in an amount less than 10% by weight, and preferably less than 5 % by weight, and more preferably less than 1 % by weight of the
polymer blend compositions. However, once again, for medical applications, preferably the use of such polymers is avoided, and the various layers are preferably
substantially free of such additional polymers.
Preparation of Polymer Blends The blended polymer compositions of the present invention can be prepared by techniques well-known to those skilled in the art. For example, a particularly useful procedure is to intimately mix the polymers using conventional melt mixing equipment
such as a mill, a Banbury, a Brabender, a single or twin screw extruder, continuous mixers, kneaders, etc. For example, the polymers may be intimately mixed in the form of granules and/or powder in a high shear mixer. One preferred process for
preparing the blended polymers utilizes the Farrell Compact Processor, CP-23 and CP-
57. Short residence times and high shear are readily obtained in a CP-23 and a CP-57.
"Intimate" mixing means that the mixture is prepared with sufficient mechanical shear and thermal energy to produce a dispersed phase which is finely divided and homogeneously dispersed in the continuous or principal phase.
The layers such as the cap, inner and core layers may be applied by co-extrusion, laminating, etc. , or the inner and cap layers can be applied from a solution or a dispersion of the materials in water or an organic liquid such as methylene chloride,
methyl benzene (toluene) and dimethyl benzene (xylene).
Thermoformed articles having desired shapes can be produced from each of the
blended polymer compositions of the present invention by:
(I) feeding a sheet of the blended polymer composition of the invention to
a heating station;
(II) heating the sheet to its softening point; and
(III) feeding the softened sheet to a forming station where it is thermoformed
into articles of the desired shape.
Various features and aspects of the present invention are illustrated further in
the examples that follow. While these examples are presented to show one skilled in
the art how to operate within the scope of this invention, they are not to serve as a
limitation on the scope of the invention where such scope is only defined in the claims.
Moreover, in the following examples, preparation of blends, compounds, molded
specimens and multilayer sheets are illustrated. These examples serve merely as
illustrative embodiments of the present invention and are not to be considered limiting.
Unless otherwise indicated in the following examples and elsewhere in the
specification and claims, all parts and percentages are by weight, temperatures are in
degrees centigrade and pressures are at or near atmospheric.
Example 1
A blended composition for use as the core layer made in accordance with the
present invention as shown in Table 1 is prepared on a Farrell Compact Processor, CP-
57 at a mixer rotor speed of about 500 rpm and extruded at about 220 °C into strands
which are passed through water bath and air wipe prior to pelletizing.
Table 1
Component Weight %
Fina Z Polymer Z9450 69.90
(Random Polypropylene Copolymer)
Engage 8100 PR 30.00
(Ethylene Copolymer, Metallocene)
Ethanox 330 0.10
(Antioxidant, Albemarle)
Example 2
A random copolymer of polypropylene available from Rexene Products of
Dallas, Texas, under the trade designation PP 23M10 is provided for use as the cap
layer.
Example 3
A flexible homopolymer of polypropylene available from Rexene Products of
Dallas, Texas, under the trade designation WHO is provided for use as the inner or
core layer.
Example 4
A multilayer structure is made by co-extruding polymer compositions from
Examples 1, 2 and 3 above. The polymer composition of Example 1 is placed in an
extruder and heated to a melt temperature 220° C. The extruder is operating at 100 rpm
and has a head pressure of 2000 psi. The composition of Example 2 is prepared in a
co-extruder. The co-extruder is operating at 125 rpm and has a head pressure of 1750
psi. The composition of Example 3 is prepared in a second co-extruder. The second
co-extruder is operated at 125 rpm and a head pressure of 1750 psi. The polymer compositions from all three extruders are extruded to a co-extrusion feed block where the layers are brought together and then made to flow through a sheet die at 205 °C. The co-extruded sheet then passes between a series of polish rolls which both cool and
impart a surface to the sheet. The polymers form a multilayer sheet.
Example 5
A multilayer structure from Example 4 is placed in a standard vacuum forming equipment. The sheet is heated to 177°C until the sheet sags about 6 to 13mm. The mold is closed to form a thermoformable article.
While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the
scope of the appended claims.